1. Field of the Invention
The technical field of the present invention relates to a semiconductor device using an oxide semiconductor. In particular, the technical field of the present invention relates to a semiconductor device including a transistor using an oxide semiconductor.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electrooptic device, a semiconductor circuit, and electronic equipment are all semiconductor devices.
2. Description of the Related Art
Transistors which are used for many liquid crystal display devices and light-emitting display devices typified by flat panel displays have been formed over glass substrates and using a silicon semiconductor such as amorphous silicon or polycrystalline silicon.
Instead of the silicon semiconductor, a technique in which an oxide semiconductor is used for transistors has attracted attention.
Examples of the oxide semiconductor include zinc oxide, which is one-metal oxide, and In—Ga—Zn-based oxide, which is a homologous compound. Patent Documents 1 and 2 disclose techniques in which such an oxide semiconductor is used to form transistors as switching elements and the like in pixels of a display device.